Problem: Simplify the following expression: $x = \dfrac{3a}{8} + \dfrac{a}{5}$
Answer: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $8$ and $5$ $\lcm(8, 5) = 40$ $ x = \dfrac{5}{5} \cdot \dfrac{3a}{8} + \dfrac{8}{8} \cdot \dfrac{a}{5} $ $x = \dfrac{15a}{40} + \dfrac{8a}{40}$ $x = \dfrac{15a +8a}{40}$ $x = \dfrac{23a}{40}$